Identification documents such as passports or identification cards are nowadays often equipped with means for wireless communication. For example, since 2007 the U.S. government has been issuing e-passports (electronic passports) only, which include a contactless integrated circuit in the back cover. The integrated circuitry stores the data which is visually displayed on the photo page of the passport together with a digital version of the photograph of the passport holder. With the help of facial recognition technology, the digital photograph may be used for biometric comparison at international borders.
U.S. citizens crossing the border, for example to Canada or Mexico, are required to have both a passport and a further personal identification card, a so called passport card. In order to wirelessly read out data from e-passports, HF systems are employed, whereas the read out of personal identification cards, such as the passport card, is based on UHF systems. Both documents carry identification numbers which are verified during border crossing. Care has to be taken that the verification process of the two documents does not take place at the same time, which may, for example, entail both documents accessing the same database at the same time in order to verify the checked document. Therefore, simultaneous verifications of both kinds of may need to be avoided. In addition, the citizen crossing the border is required to carry both documents as both verification systems are used independently from one another.